The present invention relates generally to roofing plates for securing a water resistant roofing membrane to a roof deck, and specifically to a roofing plate configured and adapted to prevent such a roofing membrane from slipping out from underneath the roofing plate.
In certain modern roofing installations of commercial and factory buildings having a flat roof design, a layer of insulation is placed on a generally corrugated steel roof deck, and is then covered with a single ply thermoplastic roofing membrane to protect against the elements. A common method of securing the roofing membrane to the roof is to attach the edges of a long sheet of the membrane to the deck using fasteners passing through the insulation. The most common fastener is an elongated screw passing through a plate or washer. These fastener assemblies (screw plus plate) are placed at regular intervals along the membrane edge. Once a sheet of roofing membrane is thus secured, another sheet is laid parallel to, and with its edge overlapping, the edge of the already secured sheet. In this manner, the fastened plates are covered by the edge of the second membrane sheet in the overlapped region. Next, a heat gun is used to heat the top and bottom of the overlapping sheets to the melting point, and they are pressed together. As the membrane sheets cool, they become bonded together. This process is continued until the entire roof is covered with the roofing membrane.
It has been found that, because the membrane is exposed to the elements, it may at times be subject to high velocity winds blowing across the roof which cause uplift forces. These forces cause the membrane to billow upwardly. As this occurs, the membrane tends to pull up and exerts an upward force on one edge of the plate, which causes the plate to shift or rock backwards in the direction away from the force. Rocking prevents the fastener from being pulled out of the roof by alleviating this edge-directed force, but it also allows the membrane to slip from underneath the plate, and at a certain point, causes the membrane to tear around the fastener.
In commonly assigned U.S. Pat. No. 5,797,232 to Larson, the disclosure of which is incorporated by reference herein, a roofing plate is disclosed which, in conjunction with a fastener such as a screw, is adapted to "rock" onto its longitudinal sides, which are parallel to the edge of the roofing membrane, as the membrane billows upwardly, thereby alleviating stress on the head of the fastener. The Larson plate also has a generally oblong configuration which is adapted to distribute the load to a broader area to prevent the membrane from tearing, as one of the sides of the plate is pressed into the membrane as it rocks. Moreover, the broader two sides of the plate are provided with gripping formations, such as a series of notches, to grip the membrane as it rocks to prevent the membrane from slipping relative to the plate and tearing around the fastener.
While the oblong configuration of the Larson plate distributes stress along its longer sides and prevents the sides of the plate from cutting into and tearing the membrane, the corners of the plate concentrate a significant amount of stress on a small portion of the membrane as the membrane is uplifted, and consequently, weaken and tear the roofing membrane. Moreover, the longer sides of the Larson plate are adapted to be aligned parallel to the edge of the roofing membrane to distribute the load to a broader area, and to enable the gripping formations to grab the membrane when the membrane is uplifted. However, the plates often spin away from the required parallel alignment with the edge of the roofing membrane when the plate is being installed or when the plate is inadvertently kicked by an installer. Additionally, the Larson roofing plate is relatively expensive to manufacture due to its size, and thus disadvantageous from a commercial perspective.
Thus, it is a first object of the present invention to provide an improved roofing plate for attaching a roofing membrane to a roof that is relatively inexpensive to manufacture, and yet sufficiently strong to resist permanent bending and deformation.
Another object of the present invention is to provide such an improved roofing plate having elongated sides, but yet have corners that do not tear the roofing membrane.
Yet another object of the present invention is to provide such an improved roofing plate which is configured keep the plate in desired alignment with the edge of the roofing membrane.